Auto pencil marks
Warn when leaving page
Show mistakes when checking
Objective / Rules - You have to complete the grid such that every row and column contains the numbers 1 to 4 (each number appears exactly once). - The arrows on the grid are less-than and greater-than signs, and always point to a smaller number (e.g. 1 < 4, 3 < 5, 2 > 1). - The Hard puzzles can be quite hard and often require the more advanced Sudoku techniques.
Keyboard Usage[only when your cursor is in the grid] Note: not all options work on all browsers. A = auto-pencil marks (or click the check box below the puzzle). CTRL + arrows = move around the grid. SHIFT + number = highlight all squares with that number as a pencil mark [SHIFT+0 to clear].
Mouse Usage Clicking an less-than or greater-than sign will change its colour, very useful when you know the sign has been satisfied.
Checking If you click 'Check' the system will check for incorrect squares. If 'Show mistakes when checking' is checked they will be marked in red. There are two types of error checked for: 1. A single number that isn't the same as the solution. 2. Multiple numbers that don't contain the solution number.
Uniqueness Each puzzle has exactly one solution, which can be found using logic alone and no guesses are ever required. If you think you've found another solution, then please double check the rules. If you still think you've found another solution, then please email us and we'll try to help.